Bearings are devices that permit constrained relative motion between two parts. Rolling element bearings comprise inner and outer raceways and a plurality of rolling elements (balls or rollers) disposed there-between. For long-term reliability and performance it is important that the various elements have resistance to rolling fatigue, wear and creep. An important characteristic of bearing steels is the hardenability, i.e. the depth up to which the alloy is hardened after putting it through a heat-treatment process.
An example of a type of bearing steel is DIN 1.3536 (100CrMo7-3(W5)). There is still room for improvement, however.